#include <bits/stdc++.h>
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
using namespace std;
typedef long long int ll;
typedef pair<int,int> P;
#define yn {puts("NO");}else{puts("YES");}
#define MAX_N 200005

int main() {
    int h,w;
    cin >> h >> w;
    string s[h];
    rep(i,h)cin >> s[i];

    int tate = 0;
    int yoko = 0;
    rep(i,h){
        int flag = 0;
        rep(j,w){
            if(s[i][j] == '0'){
                flag |= 1;
            }else{
                flag |= 2;
            }
        }
        if(flag != 3)yoko = 1;
    }
    rep(j,w){
        int flag = 0;
        rep(i,h){
            if(s[i][j] == '0'){
                flag |= 1;
            }else{
                flag |= 2;
            }
        }
        if(flag != 3)tate = 1;
    }

    if(h == 1){
        if(yoko)yn;
    }else if(w == 1){
        if(tate)yn
    }else{
        if(tate && yoko)yn;
    }
    
    return 0;
}